Electrochemical oxidation of organosilicon compounds I. Oxidative cleavage of carbon-silicon bond in allylsilanes and benzylsilanes

Tetrahedron Printed in

Letters,Vol.27,No.29,pp Great Britain

ELECTROCHEMICAL

3373-3376,1986

OXIDATION

OXIDATIVE

OF ORGANOSILICON

CLEAVAGE

Yoshida, *

Jun-ichi of

Organic 3-3-138,

Summary:

presence

of

alcohol,

carbon-silicon

oxidation carboxylic

bond

and

of

of

acid,

formation

and

of

the

lsoe

Osaka

City

Osaka

558, JAPAN

allylsilanes

and

or

I.

BOND

Sachihiko

Science,

Sumiyoshi,

+ .OO Ltd.

BENZYLSILANES

Murata,

Faculty

Sugimoto,

Electrochemical

AND

Toshiki

Chemistry,

COMPOUNDS

OF CARBON-SILICON

IN ALLYLSILANES

Institute

0040-4039/86 $3.00 Pergamon Journals

water

benzylsilanes

resulted

corresponding

University,

in

ether,

in

the

of

the

cleavage ester,

or

alcohol,

respectively. The

purpose

oxidation The

of

basic

works

of

two

ideas

suggest

the

definite

such

chemical

oxidation3 is

looses

for

be such

a

to

the

giving

rise effect

further

oxidized

cationic

to

disclose

observations

our

via

the

to

also

the

parent cation

the

under a

indeed

occur

exactly

be

on

of

the

the

(2)

the

is

benzyltrialkylsilanes. and toward

n-system.

radical

to

in some

as

bond.697

Introduction

of

“umpolung”

reaction

does

as expected

(eqs

For is

w

&N/OR

of

1 and 2).

(1)

(2)

3173

to into

organosilicon

-2e

ROH

benzylic

nucleophiles

ROH

SiMe,

is

“super

expected

-2e

WSiMe,

cases,

a

compounds.g The

of

group

act

species

electro-

oxidation

which,

carbon-silicon

for

the toward

trimethylsilyl

expected

method

experimental2

Electrochemical If

produced

electrochemical

susceptible

intermediate

conditions.

useful

group

quite

radical.4

group

(3) Thus

provide

8-silyl

to

radical

silyl

will

of

system.

ally1

cleavage

expected.

cation

seem

the

give

selective is

species8

the

proton,

effect

group

with

to

allylic to

donating 8-silyl

proceed

proton

similar

proton”5 cases

having

compared

allylic

substituted

is

electron

rr-systems

suggested

an

letter

allyland of organosilicon compounds, i.e. types behind this work were as follows. (1) Both theoreticall

Therefore olefins

this

3374

Oxidation of Allylsilanes and Benzylsilanesa Table I. Electrochemical _-----~~___----_____---__----~~____----_---~~~__----------~__-----------~~~~~ R'OH

RSiMe3

yield

product

method

(W)b

-._----_

ASiMe

MeOH

A

3

G

*OMe

OMe (68

EtOH

56 *OEt OEt

(63 : 37) 62

B Jw+

JNJNOH OH

AcOH

: 32)

B G

H20

69

(60 : 40) 26c

B /k/+9

*ok OAc (63 : 37)

MeOH

PhwSiMe,

B Ph

(76)

PhwOMe

\ ‘r‘ OMe

MeOH

(63

: 37) quantitative

A

SiMe, OMe OMe (61 SiMe,

SiMe,

MeOH

A

MeOH

A

Me,Si

: 39) OMe

OMe

(91)

quantitative

Me ,Si

SiMe,

MeoH

72

A

OMe

OMe

SiMe,

MeOH

69

A

__--___-_____________--_______--___--_______----_-___---__-----~-_---__-

-----

compound (1.0 organosilicon with an a Reactions were normally carried out the M EtqNOTs/MeCN in mmol) in 0.2 M EtqNOTs/MeOH (method A) or in 0.2 acid (25 mmol) (method B) using presence of an alcohol, water, or acetic b Isolated Passed electricity was normally 2.1 Fjmol. carbon rod electrodes. A mixture of VPC. c determined by were Yields in parentheses yields. linalool

and geraniol

was also

produced

in 31% yield.

3375

A

typical

procedure

Geranyltrimethylsilane

(1.0

p-toluenesulfonate carbon

rod

mA),

aqueous

linaloyl also water B).

in

electrodes.

After

2.1

F/mol

work-up in

be

allylsilane

with

the

presence

the

former

the

of

with

several

the

to

no

The

observed

interesting.

Only

aromatic moiety

was

obtain bond

for the

to

more

ends

a

by

the

oxygen

allyl-

reaction

insight

Thus

data

the

of

(Method

was

not is

group.lO

Another cleaved

in

reactivity

the

ally1

moiety

not

seem

to

hydroxyl,

moiety

of

carbon

in

depend

and

of

acetoxyl

geranylsilane

was

electrochemical onto

of

the

nucleus

in

predominant.

A

method

benzylic was

under

position

detected.

similar

exclusively High

chemo-

p-(trimethylsilyl)benzyltrimethylsilane

bond

was

into

the

reaction

allyldimethyloctylsilane in

by the

should

(Scheme or

to of

observation

higher

does

ally1

aromatic

carbon-silicon

deeper

induced

more

scheme

This

selectively

ethoxyl,

cleaved

without

mechanism

the

82

% yield

attack

of

the

(eq

was 3), l2

alcohol

is

affecting

the

I)

seems

benzylsilane

nucleophile

on

be

implying

silicon

in

that

the

the

silyl

methanol

of

to

carbon-silicon

Me CgHI7SiOMe

be

produces cleaves

(3)

he

accumulated to

fate

electrolyzed

on silicon.

MeOH

the

alcohol presence

in geranylsilane

much

substituted

t

from

of was

allylsilanes.

introduced on

both

-2e

following

an

the

6-silyl

indicating

the

other

oxidized

attack

methoxydimethyloctylsilane

Although

10

bond.

get

was

reaction

respectively

was

regioselectivity of

the

for

was

the

benzyl

investigated.

cleavage

of bond

Methoxyl,

ends on

also

from

carbon-silicon

In order

attack

nucleophile

derived

selectivity

both

observed

were

oxygen

products

ability

the

to

employed.

the

was

Benzyltrimethylsilanes and

of

in

conditions.

carbon-silicon

11 The

intermediate.

6 : 4 ratio.

The

two

: 32 mixture

68

A). The

esters, bond

the

bonds,

with current,

allylsilanes.

double

under

a

25 equiv

or

follows.

equipped

(constant

reaction

several

donating

introduced

nucleophile

regioselectivity

conditions.

of

the

as

tetraethylammonium

(Method

presence

for

ally1

passed

afforded

alcohols

carbon-hydrogen was

cation

of

introduced

approximately

of cell

fashion

oxidized

the

solution undivided was

carbon-carbon

electron

that

ally1

the

obtained

was

M

is

latter.

ally1

were

is

nucleophile

nature

similar

note

the

oxygen

groups

moiety

in

allylsilanes

an

distillation

similar

simple

of

in 69% yield

corresponding

results the

suggested

to

than

consistent

the

in

electricity

ether

a

the

that

of

solvent

In

afforded

0.2

placed

bulb-to-bulb

as

ether.

oxidation

in

was

methyl

acetonitrile

noted

feature

by

geranyl

1 summarizes

accord

the

and

acid

Only

The

followed

ether

should

important

on

ml)

acetic

affected.

dissolved

(10

out

Table It

mmol)

corresponding

or

electrochemical

methanol

carried the

the

in

methyl

obtain

for

before

reasonable cation the

radical

elucidation at

present.

of

Initial

intermediate.

carbon-silicon

bond

the

mechanism, electron

Selective to

give

the

the

transfer attack

of

allyl-

or

3376

benzyl

radical.

molecule

of

Further the

oxidation

oxygen

gave

nucleophile

the

to

corresponding

produce

the

cation

final

which

reacts

with

another

product.

Scheme I

ROH NSiMe,

__..?_+

NSiMe,

)-

f

*

-e+

-II+

-MegSiOR, ROlI +------+

NOR -II+

Further

studies

in

this

reaction.

mechanism

of

References

and Notes

(1) (a)

Horn,

Pillot,

(2) (a) (3)

P.; J.

J. Am. -Chem. Electrochemical

(a)

Fueno,

T.;

Chemistry

as I.

(6)

Oxidative

cleavage

Chem.

T.;

in

(8)

the

1985,

Metal-Carbon

Reactions

of

Bond”,

Berlin,

1983.

W. (b)

and

6544.

the

n

51.

(b)

Bock,

presence

of

I. L. Tetrahedron 1972, a

7892.

(c)

2313.

the

(b)

detailed

Deleris,

H.;

G.;

W.

ion

is

1976, 2469.

&

Shono,

Kaim,

fluoride

(b) Yoshida, T.

Springer-Verlag:

bond,

see:

J.;

Kumada,

references

(a)

Tamao, M.

K.:

Kanbe,

“Electroorganic

Berlin,

1984.

F.

compounds

R.;

with

see:

Patai,

C. S.

for

E.

W.

“Silicon

Fujita,

E.

Tetrahedron

T.:

Akita,

1983, a

Tetrahedron

J.

Sakurai,

Pickett

Ed.

electrophiles

Reagents

Kakui,

M.;

983.

H.

Ed.

(b) Ellis

therein.

bonds,

Hartley,

K.;

Chemistry”,

cited

metal-carbon

Colvin,

in

i?%

and

2215.

Bioorganosilicon

“Silicon

P.

105,

scope

83.

Yoshida,

and

of

organosilicon

Weber,

are

Organic in

in

Wiley: well

known,

Chemistry 1985.

for

example,

Springer-Verlag,

Synthesis”,

Organic

“The

Chichester,

Synthesis”,

Butterworths,

1981.

Ochiai,

M.;

(10) Oxidation anodic vs.

R.;

1983,

Synthesis”,

carbon-silicon

cleavage

see:(a)

1981,

Rev.

of

Chichester,

London, (9)

Sot.

a

Sot.

1977,

full

1974,

m.

Knunyants,

Chem.

in Organic

“Organosilicon

(7) Electrochemical of

I. N.;

L Am.

Tool

Kanatani,

K.

Horwood:

A.

w.

the

1980,

tetraalkylsilanes

Rozhkov,

a New

Fleming, Iwahara,

4429.

of

J. Org. Chem.

(5)

Tamao,

Organomet.

1980, 102,

Ikeda, T.

J-

delineate

Tetrahedron, Chem.

I. Y.;

T.;

hopefully

Am_

oxidation

Alyev,

Shono,

C.

L

Sot.

N.

J.

C.

may

J.

Rayez,

Giordan,

known: (4)

Murrell,

M.;

J.

progress

Arimoto, potential

than

DeWolfe,

(12)

From

R.

a

venient tions. (Received

of

those

Ag/AgCl)

(11)

M.;

under H.;

synthetic method

Organic in

geranyltrimethylsilane

of

trisubstituted

the

Young, point for

employed

using

such

as

in the

Rev.

1956, s

this

reaction

is

of

allylsilanes

alkoxysilanes,

8 May 1986)

see

is

much

(Ep

=

less

1.85

V

753. since

alkoxysilanes ref

Ag/AgCl)

reaction.

interesting,

to

4491.

2-methyl-2-butene present

Chem.

view

conversion

synthesis Japan

W. G. of

1981, g

(Ep = 1.30 V vs.

olefins

conditions

&

6b

and

it

provides

a con-

under

neutral

condi-

references

cited

therein.